Sunday's confrontation between an armed Hamas cell and Palestinian Authority policemen in Kalkilya shows that the Islamic movement still has a military presence in the West Bank - one that it is hoping to use to topple Mahmoud Abbas's regime there. PA security officials said the two Hamas operatives who were killed in the clash, Muhammad Samman and Muhammad Yassin, headed a cell that possessed large amounts of weapons, including explosives and automatic rifles, some of which had been hidden in a basement of a mosque in the city. The weapons, according to the officials, were supposed to be used...